What Is a Smoke Compartment?

By Valerie Ziavras

Compartmentation is a passive fire protection feature intended to minimize the area impacted by an incident. There are two different types of compartments: smoke compartments and fire compartments.

Smoke compartmentation may be required by a building code, fire code, life safety code, or some other code. This blog will focus on smoke compartmentation as it is required by NFPA 101^®, Life Safety Code^®.

A smoke compartment is defined in NFPA 101 as “a space within a building enclosed by smoke barriers on all sides, including top and bottom.” Smoke compartments are intended to restrict the spread of smoke from one area of a building to another. Fire compartments, on the other hand, are formed by fire barriers on all sides and are intended to restrict the spread of fire from one area of a building to another. To learn more about fire compartments, check out a related blog about fire barriers.

Smoke barriers can also serve as fire barriers, provided they meet the requirements for both, so it is possible for a smoke compartment to also serve as a fire compartment. However, both sets of requirements need to be met.

Although a smoke barrier is intended to restrict the movement of smoke from one area of a building to another, it does not guarantee tenability throughout the adjacent smoke compartment. The adjacent smoke compartment should be safer than the smoke compartment containing the fire. This allows occupants to move from the smoke compartment containing the fire to the adjacent compartment; however, they may need to eventually evacuate the adjacent smoke compartment as well.

Where is smoke compartmentation required?

Certain occupancies require buildings to be subdivided into separate smoke compartments. These requirements can typically be found in the XX.3.7 section of the occupancy chapter in NFPA 101.

Examples of occupancies that require buildings to be subdivided using smoke barriers include new and existing health care occupancies (like hospitals), new and existing ambulatory health care occupancies (like day surgery centers), and new and existing detention and correctional occupancies. One factor these occupancies have in common is that a defend-in place strategy is typically used. This makes compartmentation even more important than in other occupancies that use a total evacuation strategy, since the first step during an emergency is to relocate building occupants.

Typically, where smoke compartments are required, the occupancy chapter also outlines minimum accumulation space requirements. This ensures that if relocation needs to happen there is enough space in both compartments to accommodate the occupants.

In some cases, the smoke barrier required will also need to have a certain fire-resistance rating. Simply because a smoke barrier requires a fire-resistance rating does not automatically make it a fire barrier. However, there are cases where a smoke barrier may also be required to be a fire barrier, such as if the smoke barrier wall is also being used as a horizontal exit. In that case, the wall would need to be constructed to meet both the smoke barrier requirements and the fire barrier requirements.

Smoke compartment construction

Smoke compartments are created using smoke barriers. Unlike fire barriers—which ultimately get their fire-resistance rating through prescribed analytical methods or tests such as ASTM E119, Standard Test Methods for Fire Tests of Building Construction and Materials, or UL 263, Fire Tests of Building Construction and Materials—smoke barriers do not have a specific standard they must be tested to. There are, however, several requirements related to the continuity of smoke barriers, opening protectives, ducts and air-transfer openings, penetrations, and joints.

Continuity

Smoke barriers must be continuous from an outside wall to an outside wall, from a floor to a floor, from a smoke barrier to a smoke barrier, or any combination of those. It should be noted that where a smoke compartment is formed using an outside wall or roof, it is not intended for the outside walls or roofs or openings to be capable of resisting the passage of smoke. Since smoke that passes through those walls/roofs will be going to the outside and building occupants will not be relocated to those areas, the restriction of the passage of smoke is less of a concern.

Smoke barriers must be continuous through all concealed spaces, such as the interstitial spaces formed by a drop ceiling. Smoke barriers are permitted to terminate below the interstitial space if the construction assembly forming the bottom of the ceiling provides resistance to the passage of smoke equal to that provided by the smoke barrier.

Other considerations

The integrity of the smoke barrier is essential to restricting the passage of smoke from one compartment to an adjacent compartment. This means that components that are needed for the building to function, such as doors, fire windows, ducts, air-transfer openings, and penetrations from cables, conduits, tubes, and similar items need to be properly protected. For example, doors must be self-closing or automatic closing and they must latch.

Duct and/or air-transfer openings require dampers to protect adjacent compartments from smoke transfer. However, there are certain situations where dampers are not required. One example is where air inlet and outlet openings in ducts are limited to one smoke compartment.

Like openings, penetrations provide opportunities for smoke to pass from one smoke compartment to another so proper protection is also required. In new construction, penetrations must be protected by an approved through-penetration firestop system that meets the requirements of UL 1749, Fire Test of Penetration Firestops, for air leakage.

The joints where smoke barriers meet other smoke barriers or the floor or roof deck above or outside walls could present a potential pathway for smoke to get into an adjacent smoke compartment. Therefore, again, proper protection is required. One example of protection required is in new construction; joints made within, between, or at the perimeter of smoke barriers must be protected with a joint system that is tested for air leakage in accordance with UL 2079, Tests for Fire Resistance for Building Joint Systems.

Key takeaways

Smoke compartments, and thus smoke barriers, play an important role in building compartmentation, especially for occupancies that depend on a defend-in-place strategy. Ensuring the proper construction of smoke barriers, including the continuity, openings, duct and air-transfer openings, penetrations, and joints, is critical to their effectiveness.

Without the proper protections in place, the smoke barrier may not be capable of restricting the passage of smoke to an adjacent compartment, potentially endangering building occupants.

SOURCE: NFPA